1. Field of the Invention
This invention relates to a variable displacement pump, more particularly to a variable displacement pump for pressurization of fuel/lubricant oil to be supplied into an engine.
2. Description of the Related Art
A conventional oil pump is employed to supply fuel/lubricant oil into an engine in a vehicle system, and generally includes an internal rotary member and an external rotary member which are driven by the engine to rotate so as to pump the fuel/lubricant oil into the engine. The lubrication requirements of the component parts of the engine vary with the operation speed of the engine, and the variation in the lubrication requirements and the variation in the rotational speed of the engine are generally nonlinear. For example, when the rotational speed is increased, the lubrication requirement is decreased, thereby resulting in an over supply of fuel/lubricant oil into the engine. Thus, a variable displacement pump is proposed as a fuel/lubricant oil pump.
A conventional variable displacement pump is disclosed in WO 2007/087704, which includes a control slider, an engine control unit (ECU), and a biasing member. When the pressurized fuel/lubricant oil has a relatively higher pressure, the control slider is actuated to move by means of an electrical control of the ECU so as to reduce the supply of fuel/lubricant oil. When the pressure of the pressurized fuel/lubricant oil is lowered to a predetermined value, the control slider is urged by the biasing member to return to its original state. Thus, fuel/lubricant oil can be supplied as the lubrication requirement of the engine.
Another type of the conventional variable displacement pump includes a control slider which is displaced in accordance with the working pressure of the pressurized fuel/lubricant oil, and a biasing member. However, since there are many clearances around the biasing member, the pressurized fuel/lubricant oil tends to flow into the clearances and accumulates therein, which may adversely affect the operation of the biasing member to result in unsteady operation of the pump.